Crawling The Deep Web
A vast amount of Web pages lie in the deep or invisible Web. These pages are typically only accessible by submitting queries to a database, and regular crawlers are unable to find these pages if there are no links that point to them. Google's Sitemaps protocol and mod oai are intended to allow discovery of these deep-Web resources.
Deep Web crawling also multiplies the number of Web links to be crawled. Some crawlers only take some of the -shaped URLs. In some cases, such as the Googlebot, Web crawling is done on all text contained inside the hypertext content, tags, or text.
Strategic approaches may be taken to target deep-Web content. With a technique called screen scraping, specialized software may be customized to automatically and repeatedly query a given Web form with the intention of aggregating the resulting data. Such software can be used to span multiple Web forms across multiple Websites. Data extracted from the results of one Web form submission can be taken and applied as input to another Web form thus establishing continuity across the Deep Web in a way not possible with traditional web crawlers.
Read more about this topic: Web Crawler
Famous quotes containing the words crawling, deep and/or web:
“The wind and the rain, gives this place a gleam that just isn’t natural. And the ground, alive with crawling things, crawling death.”
—Edward D. Wood, Jr. (1922–1978)
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Grows more deep day after day,
His empty heart is full at length
But he has need of all that strength
Because of the increasing Night
That opens her mystery and fright.”
—William Butler Yeats (1865–1939)
“Ye whose clay-cold heads and luke-warm hearts can argue down or mask your passions—tell me, what trespass is it that man should have them?... If nature has so wove her web of kindness, that some threads of love and desire are entangled with the piece—must the whole web be rent in drawing them out?”
—Laurence Sterne (1713–1768)